Regenerative heat exchange process for formation of combustible gas



Dec.

D. E. ELLIOTT REGENERATIVE HEAT EXCHANGE PROCESS FOR FO TION OF COMBUSTI GAS ed July 21, 195

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A tl'orn ays United States Patent REGENERATIVE HEAT EXCHANGE PROCESS FOR FORMATION or COMBUSTIBLE GAS Douglas Ernest Elliott, We'yhridge, England, assignor to Power Jets (Research and Development) Limited, London, England, a British company Filed July 21, 1955, Ser. No. 523,517 Claims priority, application Great Britain July 29, 1954 SClaims. (01.48-206) According to the co-pending patent application Serial No. 488,010, now US. Patent, 2,866,697, a vessel for high temperature gases is heat insulated from the gases by a very thick layer of a partly molten mass such as slag; the vessel has rotary walls shaped to retain a thick layer of slag, and driving means for rotating the walls at such a speed as to provide the centrifugal force necessary for building and maintaining this layer. The thickness of the layer will be several inches in depth, usually of the order of 1 ft. The inner surface of the layer will be molten, and the outer surface will be solid and at a much lower temperature which the metal walls can withstand. This makes it possible to operate with gases at a temperature greater than 1,200 C. and possibly at a temperature of 2,000 C. or more. The said co-pending application describes one particular form according to the invention of a cyclone combustion or gasification chamher.

The present invention consists in applying the same principle to a regenerative heat exchanger, by which term, as used herein, is meant a heat exchange device having an element or mass capable of absorbing and giving out heat in response to alternate hot and cool fluid flow over said element or mass. The absorption of heat by said element is referred to herein as regeneration of heat in the element. In the present instance the layer constitutes the element or mass and can be at the said high temperature, and can be a very high rate of radiant heat transfer between the mass and a gas such as steam or CO having a high emissivity. The method of treating a gaseous product, according to the invention, includes the steps of transferring radiant heat between the molten surface of a thick layer of a partly molten mass centrifugally spinning about an axis so as to define a central gas path, by directing a stream of hot gas along said gas path, withdrawing said hot gas from said gas path, and then directing a further steam of cool gas along said gas path and withdrawing said further stream of gas. Thus according to the invention a regenerative heat exchanger for gases includes a duct for the pasage of the gases, with a rotary wall shaped to retain thereon a thick layer of a partly molten mass, inside the duct and bounding the gas path, and driving means for rotating the wall about the duct axis at such a speed as to provide the centrifugal force necessary for building up and maintaining this layer. There may be valve means for causing hot gas (to be cooled) and cool gas (to be heated) to flow alternately through this rotary duct in heat transfer relationship with the layer.

The gas leaving the reaction chamber according to the said co-pending application may, and usually will, be at too high a temperature for passing through an uninsulated uncooled metal walled duct; the gas will therefore need preliminary cooling as it leaves the reaction space. Accordingly, an important feature of the present invention is the combination consisting of a reaction chamber according to the said co-pending application, a duct according to the present invention leading to the reaction 2,965,463 Patented Dec. 20, 1960 2 chamber, and another such duct leading therefrom. The reaction chamber may be such that it will operate with gas flow therethrough in either direction each of the two ducts then serving alternately as inlets: to and outlets from the reaction chamber, and flow-reversing valves are then provided at the outer ends of, or outside, the ducts. The valves are thus in the inlet for cool gas and the out-- let for cooled gas and do not come in contact with the hottest gases. Furthermore, acording to a feature of the invention the ducts and the reaction chamber may be co-axial and all rotates about their common axis. The invention is illustrated by the accompanying drawing which shows the reaction chamber and ducts in axial section.

A rotor consisting of a tube 1d (defining the alig'iied ducts 1 and 2 'with the reaction chamber 3 situated between them) is rotationally mounted substantially horiiontally in the stationary casing 4 by ball bearings 5. A ear Wheel 6 secured to tube 1a meshes with pinion 7 driven by electric motor 8. Rotary labyrinth seals 9 between the casing and the rotor at each end oppose gas leakage into the centre part 4a of the casing interior. The tube 111 has end walls 1b and 10 for retaining a thick layer of slag, wall 10 being bulged outwardly as shown and having slag-overflow notch 1d. Aligned with the apertures the end walls 1b and 1c are the ducts 10 and 11 secured to or integral with the casing. There is considerable clearance between end wall 10 and duct 11, to allow surplus slag to be thrown out and to drop into the waterfilled slag-collecting trough 12 or the casing. Inlet and outlet pipes 13 and 14 on the casing allow cooling air to be passed through the interior 4a; the air pressure therein may be high enough to oppose inward leakage of gas from the ducts 10 and 11.

Attached to duct 11 and extending axially through duct 1 into re ction chamber 3 is the fuel pipe 15, preferably water-cooled, which allows admission of fluidised powdered fuel and terminates in discharge nozzles 15a.

A continuation 10a of duct 10 (indicated in the drawing by line 10a) is connected to valves 16 and 17; continuation 11a of duct 11 is connected to valves 18 and 19. The duct 20 for incoming cold air or other gas is connected to valves 16 and 18; the outgoing duct 21 for cooled gas is connected to valves 17 and 19.

In operation. with tube 1a rotating, and for the typical process of gasifying coal, oxygen and steam enter by duct 21. With valves 16 and 119 closed and valves 17 and 18 open, this gaseous mixture on its way from duct 11 to the reaction chamber 3, passes through duct 1, wherein it takes up heat by radiation from molten slag already built up on the wall of tube In. The hot gases evolved in the reaction with coal from pipe 15 include hydrogen, C0, C0 and steam. This mixture passes along duct 2 giving up radiant heat to the molten slag layer and possibly adding furt er deposit to that layer. When the valves are reversed to reverse the direction of flow the incoming gas takes up heat from duct 3 and the outgoing gas gives out heat to duct 1. The centrifugally retained layer of deposit builds up to the maximum which the end walls 1b and 10 can retain, as determined by notch 1d through which any surplus passes and is flung out centrifugally. In this typical reaction, the slag formed Will be fused coal ash. but the term slag is used herein broadly as in the said copending application to include any substance evolved by the reaction to form a heat-insulating deposit on the walls. In the case of some other reaction which does not produce anything to form such an insulating layer, ash or other materials may be introduced into these ducts where they will be fused by the heat to form the layer. The hot outgoing gas will be cooled sufliciently to be handled in conventional apparatus, and the incoming gas will take up suflicient heat from the molten deposit to attain a temperature which will facilitate conducting the reaction at high temperature; in particular oxygen and steam can be raised to a temperature far above the maximum possible for oxygen in contact with metal walls.

It will be understood that the invention can be applied in other forms to various other reactions or other heating processes. By way of contrast to said prior specification which describes a vertical combustion chamber the present specification has set forth a horizontal construction but it will be understood that the invention can be applied to a vertical arrangement.

' I claim:

1. A regenerative heat exchange process for the treatment of a gas including the steps of establishing a thick centrifugally retained circumferential layer of partly molten material surrounding a central gas path, alternately directing a stream of gas to be heated into said central path at one end thereof, and withdrawing gas at the other end of the gas path, and regenerating heat in the said layer by passing hot gas in heat exchange therewith.

2. A process according to claim 1 including the step of establishing a heat evolving reaction at a region of the path intermediate the ends. 3. A process according to claim 2 including the steps of supplying steam and oxygen bearing gas together with fuel to react in said intermediate region to form combustible gas.

4. A process according to claim 2 including the step of periodically reversing the direction of flow of the gas in said path by supplying and withdrawing the gas respectively at opposite ends ofthe gas path.

5. The method of treating a gaseous product which includes the steps of transferring radiant heat between the molten surface of a thick layer of a partly molten mass centrifugally spinning about an axis and defining a central gas path by directing a stream of hot gas along said gas path, withdrawing said stream from the gas path, and then directing a further stream of cool gas along said gas path and withdrawing said further stream of gas.

References Cited in the file of this patent UNITED STATES PATENTS 397,397 Smith Feb. 5, 1889 1,377,372 Thompson May-10, 1921 1,781,934 Synder Nov. 18, 1930 2,001,083 Walter May 14, 1935 2,350,052 Luertzing May 30, 1944 2,441,528 Bender May 11, 1948 2,603,556 Miller July 15, 1952 2,680,084 Ryan June 1, 1954 2,866,697 Elliott Dec. 30, 1958 FOREIGN PATENTS 22,708 Great Britain of 1895 

1. A REGENERATIVE HEAT EXCHANGE PROCESS FOR THHE TREATMENT OF A GAS INCLUDING THE STEPS OF ESTABLISHING A THICK CENTRIFUGALLY RETAINED CIRCUMFERENTIAL LAYER OF PARTLY MOLTEN MATERIAL SURROUNDING A CENTRAL GAS PATH, ALTERNATELY DIRECTING A STREAM OF GAS TO BE HEATED INTO SAID CENTRAL PATH AT ONE END THEREOF, AND WITHDRAWING GAS AT THE OTHER END OF THE GAS PATH, AND REGENERATING HEAT IN THE SAID LAYER BY PASSING HOT GAS IN HEAT EXCHANGE THHEREWITH. 